Kappa opioid receptors have been suggested as targets for intervention for treatment or prevention of a wide array of diseases and conditions by administration of kappa opioid receptor agonists. See for example, Jolivalt et al., Diabetologia, 49(11):2775-85; Epub Aug. 19, 2006), describing efficacy of asimadoline, a kappa receptor agonist in rodent diabetic neuropathy; and Bileviciute-Ljungar et al., Eur. J. Pharm. 494:139-46 (2004) describing the efficacy of kappa agonist U-50,488 in the rat chronic constriction injury (CCI) model of neuropathic pain and the blocking of its effects by the opioid antagonist, naloxone. These observations support the use of kappa opioid receptor agonists for treatment of diabetic, viral and chemotherapy-induced neuropathic pain. The use of kappa receptor agonists for treatment or prevention of visceral pain including gynecological conditions such as dysmenorrheal cramps and endometriosis has also been reviewed. See for instance, Riviere, Br. J. Pharmacol. 141:1331-4 (2004).
Kappa opioid receptor agonists have also been proposed for the treatment of pain, including hyperalgesia. Hyperalgesia is believed to be caused by changes in the milieu of the peripheral sensory terminal occur secondary to local tissue damage. Tissue damage (e.g., abrasions, burns) and inflammation can produce significant increases in the excitability of polymodal nociceptors (C fibers) and high threshold mechanoreceptors (Handwerker et al. (1991) Proceeding of the VIth World Congress on Pain, Bond et al., eds., Elsevier Science Publishers BV, pp. 59-70; Schaible et al. (1993) Pain 55:5-54). This increased excitability and exaggerated responses of sensory afferents is believed to underlie hyperalgesia, where the pain response is the result of an exaggerated response to a stimulus. The importance of the hyperalgesic state in the post-injury pain state has been repeatedly demonstrated and appears to account for a major proportion of the post-injury/inflammatory pain state. See for example, Woold et al. (1993) Anesthesia and Analgesia 77:362-79; Dubner et al. (1994) In, Textbook of Pain, Melzack et al., eds., Churchill-Livingstone, London, pp. 225-242.
Kappa opioid receptors have been suggested as targets for the prevention and treatment of cardiovascular disease. See for example, Wu et al. “Cardioprotection of Preconditioning by Metabolic Inhibition in the Rat Ventricular Myocyte—Involvement of kappa Opioid Receptor” (1999) Circulation Res vol. 84: pp. 1388-1395. See also Yu et al. “Anti-Arrythmic Effect of kappa Opioid Receptor Stimulation in the Perfused Rat Heart: Involvement of a cAMP-Dependent Pathway” (1999) J Mol Cell Cardiol. vol. 31(10): pp. 1809-1819.
It has also been found that development or progression of these diseases and conditions involving neurodegeneration or neuronal cell death can be prevented, or at least slowed, by treatment with kappa opioid receptor agonists. This improved outcome is believed to be due to neuroprotection by the kappa opioid receptor agonists. See for instance, Kaushik et al. “Neuroprotection in Glaucoma” (2003) J. Postgraduate Medicine vol. 49 (1): pp. 90-95.
The presence of kappa opioid receptors on immune cells (Bidlak et al., (2000) Clin. Diag. Lab. Immunol. 7(5):719-723) has been implicated in the inhibitory action of a kappa opioid receptor agonist, which has been shown to suppress HIV-1 expression. See Peterson P K et al., Biochem Pharmacol. 2001, 61(19): 1145-51.
Walker, Adv. Exp. Med. Biol. 521:148-60 (2003) appraised the anti-inflammatory properties of kappa agonists for treatment of osteoarthritis, rheumatoid arthritis, inflammatory bowel disease and eczema. Bileviciute-Ljungar et al., Rheumatology 45:295-302 (2006) describe the reduction of pain and degeneration in Freund's adjuvant-induced arthritis by the kappa agonist U-50,488.
Wikstrom et al., J. Am. Soc. Nephrol. 16:3742-7 (2005) describes the use of the kappa agonist, TRK-820 for treatment of uremic and opiate-induced pruritis, and Ko et al., J. Pharmacol. Exp. Ther. 305:173-9 (2003) describe the efficacy of U-50,488 in morphine-induced pruritis in the monkey.
Application of peripheral opioids including kappa agonists for treatment of gastrointestinal diseases has also been extensively reviewed. See for example, Lembo, Diges. Dis. 24:91-8 (2006) for a discussion of use of opioids in treatment of digestive disorders, including irritable bowel syndrome (IBS), ileus, and functional dyspepsia.
Ophthalmic disorders, including ocular inflammation and glaucoma have also been shown to be addressable by kappa opioids. See Potter et al., J. Pharmacol. Exp. Ther. 309:548-53 (2004), describing the role of the potent kappa opioid receptor agonist, bremazocine in reduction of intraocular pressure and blocking of this effect by norbinaltorphimine (norBNI), the prototypical kappa opioid receptor antagonist; and Dortch-Carnes et al., CNS Drug Rev. 11(2):195-212 (2005). U.S. Pat. No. 6,191,126 to Gamache discloses the use of kappa opioid agonists to treat ocular pain. Otic pain has also been shown to be treatable by administration of kappa opioid agonists. See U.S. Pat. No. 6,174,878 also to Gamache.
Kappa opioid agonists increase the renal excretion of water and decrease urinary sodium excretion (i.e., produce a selective water diuresis, also referred to as aquaresis). Many, but not all, investigators attribute this effect to a suppression of vasopressin secretion from the pituitary. Studies comparing centrally acting and purportedly peripherally selective kappa opioids have led to the conclusion that kappa opioid receptors within the blood-brain barrier are responsible for mediating this effect. Other investigators have proposed to treat hyponatremia with nociceptin peptides or charged peptide conjugates that act peripherally at the nociceptin receptor, which is related to but distinct from the kappa opioid receptor. See: D. R. Kapusta, Life Sci., 60:15-21, 1997; U.S. Pat. No. 5,840,696 and U.S. Patent Appl. No. 20060052284.